Method of forming nano-sized MTJ cell without contact hole

ABSTRACT

Provided is a method of manufacturing a nano-sized MTJ cell in which a contact in the MTJ cell is formed without forming a contact hole. The method of forming the MTJ cell includes forming an MTJ layer on a substrate, forming an MTJ cell region by patterning the MTJ layer, sequentially depositing an insulating layer and a mask layer on the MTJ layer, exposing an upper surface of the MTJ cell region by etching the mask layer and the insulating layer at the same etching rate, and depositing a metal layer on the insulating layer and the MTJ layer.

BACKGROUND OF THE INVENTION

Priority is claimed to Korean Patent Application No. 2004-3237, filed onJan. 16, 2004, in the Korean Intellectual Property Office, thedisclosure of which is incorporated herein in its entirety by reference.

1. Field of the Disclosure

The present disclosure relates to a method of forming a nano-sizedmagnetic tunnel junction (MTJ) cell without a contact hole, and moreparticularly, to a method of forming a nano-sized MTJ cell in which acontact is formed in the MTJ cell without forming a contact hole.

2. Description of the Related Art

Flash memory is a type of nonvolatile memory that has an advantage inthat data recorded in the memory is preserved even if power is turnedoff. However, the recording speed of data in flash memory isapproximately one one-thousandth that of DRAM, and flash memory also hashigh power consumption. Also, there is, to some extent, a limit of dataerasing and writing times. Therefore, research has gone into theadvantages of the DRAM and the flash memory, that is, reading andrecording at a high speed, low power consumption, and data preservationeven if power is turned off. As a result of the research, ferroelectricRAM (FeRAM), ovonic unified memory (OVM), and MRAM have been introducedas non-volatile memory.

Magnetic random access memory (MRAM) is non-volatile memory in which amemory cell includes a magnetic tunnel junction (MTJ) that storesinformation using a tunneling magneto resistance effect. Referring toFIGS. 1A and 1B, an MTJ includes an insulating layer 200 (tunnel barrierlayer) interposed between two ferromagnetic layers 100 and 300. Datastored in the MTJ depends on the direction of magnetization, i.e.,whether the direction of the magnetization either same or opposite. Thatis, as depicted in FIG. 1A, if the directions of magnetization areparallel, the tunnel resistance of the insulating layer 200 (barrierlayer) interposed between the two ferromagnetic layers 100 and 300 isminimized, and the MTJ is in a “1” state. On the other hand, as depictedin FIG. 1B, if the directions of magnetization are anti-parallel, thetunnel resistance of the insulating layer 200 is maximized, that is, theMTJ is in a “0” state. By utilizing these unique characteristics of theMTJ, the MTJ can function as a memory cell. Hereinafter, a memory cellincluding the MTJ will be called an MTJ cell for convenience.

FIGS. 2A through 2H are cross-sectional views illustrating aconventional method of forming an MTJ cell.

Referring to FIG. 2A, an MTJ layer 220 and a hard mask layer 230 aresequentially formed on a substrate 10. After stacking a photo-resist232, on a portion of the hard mask layer 230 in which an MTJ cell willbe formed, the hard mask layer 230 is dry etched using the photo-resist232 as an etch mask. Referring to FIG. 2B, the photo-resist 232 is thenremoved.

Next, a remaining portion of the hard mask layer 230 and a portion ofthe MTJ layer 220 are dry etched (FIG. 2C), and then an insulating layer240 is deposited on the resultant product (FIG. 2D). Then, referring toFIG. 2E, a mask layer 235 for forming a contact hole 260 is coated onthe insulating layer 240, and then, a contact hole is patterned byperforming lithography using a Kr stepper. Then, referring to FIG. 2F,central portions of the insulating layer 240 and the photo mask 235 areetched, thereby forming the contact hole 260 in the middle of the MTJcell. Finally, the mask layer 235 is removed (FIG. 2G) and a metal layer250 is coated on the resultant product (FIG. 2H) to complete themanufacturing of the MTJ cell.

A memory cell formed in this manner can record and reproduce at highspeeds and has lower power consumption, and an unlimited number of datacorrections can be made.

However, for practical applications, high integration of the MRAM isessential. Therefore, the MTJ cell must have a width less than 100 nm.However, it is difficult to manufacture an MTJ cell having a width lessthan 100 nm using the present technique. If the MTJ cell is manufacturedaccording to a conventional method, a contact has to be formed afterforming a contact hole having a diameter much less than 100 nm in theMTJ cell with a width of 100 nm. Thus, it is impossible to form an MTJcell having a width less than 100 nm using conventional methods. Thesize of conventional MTJ cells developed is no smaller than 400×800 nm,which is much greater than the required size for high integration. Thatis, the applicability of conventional MRAM is very low. Moreover, whenan MTJ cell is formed according to a conventional method, a resistanceof the contact is high since the contact hole is very small, therebycausing errors during recording and reproducing data and increasingpower consumption.

SUMMARY OF THE DISCLOSURE

Embodiments of the present disclosure provide a method of manufacturingan MTJ cell having a width less than a size of 100 nm that enables highintegration of a magnetic memory.

Embodiments of the present disclosure also provide a method of forming anano-sized MTJ cell with a low contact hole resistance. The methodavoids difficulties in forming a small-sized contact hole by forming acontact without forming a contact hole.

Embodiments of the present disclosure also provide a method of forming anano-sized MTJ cell with fast and low costs by removing a process forforming a contact hole.

According to an aspect of the present disclosure, there is provided amethod of forming an MTJ cell, comprising forming an MTJ layer on asubstrate, forming an MTJ cell region by patterning the MTJ layer,sequentially depositing an insulating layer and a mask layer on the MTJlayer, exposing an upper surface of the MTJ cell region by etching themask layer and the insulating layer at the same etching rate, anddepositing a metal layer on the insulating layer and the MTJ layer.

The MTJ layer includes a base layer that is conductive, a lower materiallayer having magnetic properties, an insulating layer, an upper materiallayer having magnetic properties, and a cap layer that is conductivestacked sequentially in one embodiment.

Forming the MTJ cell region by patterning the MTJ layer comprisesdepositing a hard mask on the MTJ layer, patterning the hard mask byfirst dry etching, and forming the MTJ cell region by second dry etchingthe MTJ layer to a predetermined depth using the hard mask as an etchmask in one embodiment.

The etching the insulating layer and the mask layer comprises third dryetching the insulating layer and the mask layer at the same etchingrate, terminating the third dry etching when the MTJ cell region isexposed, and removing a remaining component of the mask layer in oneembodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present disclosurewill become more apparent by describing in detail embodiments thereofwith reference to the attached drawings in which:

FIGS. 1A and 1B illustrate a configuration of an MTJ and a principle ofrecording information using the MTJ;

FIG. 2A through 2H are cross-sectional views illustrating a method ofmanufacturing a conventional MTJ cell;

FIG. 3 is a cross-sectional view illustrating an MTJ cell according toan embodiment of the present disclosure;

FIG. 4A through 4H are cross-sectional views illustrating a method ofmanufacturing an MTJ cell according to an embodiment of the presentdisclosure; and

FIG. 5 illustrates the structure of an MTJ layer of an MTJ cell.

DETAILED DESCRIPTION OF THE DISCLOSURE

The present disclosure will now be described more fully with referenceto the accompanying drawings in which embodiments of the presentdisclosure, to which the present disclosure is not limited, are shown.

FIG. 3 is a cross-sectional view of an MTJ cell according to anembodiment of the present disclosure. Comparing the MTJ cell accordingto an embodiment of the present disclosure and the conventional MTJ celldepicted in FIG. 2H, a metal layer 250 contacts an MTJ layer 220 via acontact hole 260 in the conventional MTJ cell, but in the presentembodiment, the metal layer 50 contacts the MTJ layer 20 without the useof a contact hole. Accordingly, in embodiments of the presentembodiment, a contact surface area is greater, and a very complicatedprocess is not required for forming a contact hole.

FIGS. 4A through 4H are cross-sectional views illustrating a method ofmanufacturing an MTJ cell according to an embodiment of the presentdisclosure. More specifically, an MTJ layer 20 is formed on asemiconductor substrate 10. The semiconductor substrate 10 can becomposed of a material such as Si or SiO₂, and a thickness of the MTJlayer 20 is in a range of 400˜1500 Å.

For convenience of explanation, the MTJ layer 20 is simply depicted as asingle layer in FIG. 4, however, the MTJ layer 20 generally has a morecomplicated structure. That is, as illustrated in FIG. 5, the MTJ layer20 includes a lower material film 22, an insulating film 23, an uppermaterial film 24, and a cap layer 25 sequentially formed on a base layer21. The lower material film 22 can be a single magnetic film, but canalso include a plurality of material films including a magnetic film.For example, the lower material film 22 can be formed by sequentiallystacking a tantalum (Ta) film, a ruthenium (Ru) film, iridium/manganese(Ir/Mn) film, and a synthetic antiferromagnetic (SAF) film. A nickeliron (NiFe) film can be used instead of the Ru film. The insulating film23 for tunneling can be formed of aluminum oxide (Al₂O₃). The upper film24 can also be composed to a single magnetic film like the lower film22, but can also include a plurality of material films by sequentiallystacking a cobalt iron (CoFe) film and a nickel iron (NiFe) film. Thecap layer 25 includes a conductive film such as a tantalum film or aruthenium film. The base layer 21 on which the lower material film 22 isformed can also be a conductive single layer or a conductive multiplematerial layer. When the base layer 21 is a multiple layer, the baselayer 21 can be a Ti/TiN layer in which a titanium (Ti) film and atitanium nitride film (TiN) are sequentially stacked.

After the MTJ cell is formed, the base layer 21 is connected to a dataline (not shown), and the cap layer 25 is connected to a bit line (notshown), for example.

When the MTJ layer 20 is stacked, a region for forming an MTJ cell(hereinafter, an MTJ cell region) is formed by etching a portion of theMTJ layer 20. At this time, the width and length of the MTJ cell regioncan each be less than 100 nm. To etch the MTJ layer 20 with such aminute pattern, a hard mask 30 having a high etching selectivity withrespect to the MTJ layer 20 can be used. Another reason for using thehard mask 30 is because generally it is difficult to have a finephoto-resist coating on the tantalum or ruthenium used as a material forforming the cap layer 25 which is an uppermost layer of the MTJ layer20. The hard mask 30 can be composed of SiO₂, Si₃N₄, fluorinatedsilicate glass (FSG), phosphorous silicate glass (PSG), or boronphosphorous silicate glass (BPSG). The thickness of the hard mask 30 canbe determined according to a thickness of the MTJ layer 20, and can bein a range of 1000˜8000 Å.

When the hard mask 30 is coated on the MTJ layer 20, a photo-resist 32(or electron beam resist) with a size and pattern corresponding to theMTJ cell region is coated on the hard mask 30. FIG. 4A illustrates astate when the photo-resist 32 is coated on the hard mask 30. Then, ahard mask 30 is patterned by dry etching a portion of the hard mask 30using the photo-resist 32 as an etch mask. Referring to FIG. 4B, thephoto-resist 32 is removed by dry etching and the hard mask 30 has asize and pattern corresponding to the MTJ cell region. The etching gasused for the dry etching can be a gas such as C₂F₆, C₄F₈, or CHF₃.

Next, referring to FIG. 4C, an MTJ cell region is formed by dry etchingthe MTJ layer 20 using the hard mask 30 as an etch mask. At this time,the MTJ layer 20 is not completely etched, but is etched until the baselayer 21 of the MTJ layer 20 is exposed. That is, when the Ti or TiN, ofwhich the base layer 21 is composed, is detected, the dry etching isterminated. The base layer 21 will perform as a conductive wireconnected to a data line (not shown) and a CMOS (not shown), whichcontrols the MTJ cell, located under the MTJ cell after the MRAM ismanufactured. In this process, a small portion of the hard mask 30 mayremain on the MTJ cell region, but this has no effect on the finalproduct.

In more detail and referring to FIG. 5, the cap layer 25, the uppermaterial film 24, the insulating film 23 and the lower material film 22are sequentially etched using a predetermined plasma etching process. Inthis process, the etching conditions must be adjusted according to thematerial film to be etched. This can be achieved by independentlycontrolling the composition of mixed gas used as an etching gas and abias power applied to the substrate. At this time, the etching gas,which does not include chlorine (Cl₂), is a gas having a predeterminedmixing ratio between a main gas and an additive gas. The main etchinggas and the additive gas may be BCl₃ and Ar, respectively.

After forming the MTJ cell region, referring to FIG. 4D, an insulatinglayer 40 composed of SiO₂ or Si₃N₄ is formed on an exposed surface ofthe MTJ layer 20 using a plasma enhanced chemical vapor deposition(PECVD) method or a magnetron sputtering method. The insulating layer 40insulates a metal layer 50 from other elements except the cap layer 25when the metal layer 50 is formed. Therefore, a height of the insulatinglayer 40 (that is, the minimum height of the insulating layer 40 in FIG.4D) formed outside the MTJ cell region (that is, the insulating layer 40coated on the base layer 21 of the MTJ layer 20) has to be greater thana height of the cap layer 25 in the MTJ cell region.

Then, referring to FIG. 4E, a mask layer 35 is coated on the insulatinglayer 40. The mask layer 35 is composed of a photo-resist such aspolymide or an electron beam resist for dry etching in a subsequentprocess. The mask layer 35 can have a uniform height sufficient for asubsequent etching process.

Then, referring to FIG. 4F, the insulating layer 40 and the mask layer35 are etched at the same etching rate by dry etching. That is, theetching selectivity of the insulating layer 40 with respect to the masklayer 35 is 1:1. To etch the insulating layer 40 and the mask layer 35at the same etching rate, a proper etching gas must be used for the dryetching. When the insulating layer 40 is composed of SiO₂ or Si₃N₄, C₂F₆or C₄F₈ is used as a main gas and Ar or 02 is used as an additive gas.The dry etching is terminated at the cap layer 25, which is theuppermost layer of the MTJ layer 20. That is, when the Ta or Ru which isa component of the cap layer 25 is detected during etching, the etchingis terminated.

After completing the dry etching, a portion of the mask layer 35remaining on the etched surface is removed by dry etching or organiccleaning so that the metal layer 50 can be formed in a subsequentprocess. At this time, the dry etching or organic cleaning must removeonly the remained photo-resist 32 or an e-beam resist and not affect theinsulating layer 40 and the MTJ layer 20. Since the mask layer 35 is apolymer composed of elements such as C, H, and O, the mask layer 35 isremoved by producing volatile material such as CO or CO₂ in ashingequipment using oxygen. In the present embodiment, since the insulatinglayer 40 and the mask layer 35 are etched at the same etching rate, theinsulating layer 40 and the MTJ layer 20 form a planarized surface asdepicted in FIG. 4G.

Then, referring to FIG. 4H, a metal layer 50 composed of Ti, TiN, Ta, orAl is formed on the insulating layer 40 and MTJ layer 20 using asputtering method. As described above, a relatively wide contact isformed between the cap layer 25 of the MTJ layer 20 and the metal layer50 without forming a contact hole.

As described above, a method of manufacturing an MTJ cell according tothe present disclosure enables the manufacturing of a MTJ cell having awidth of 100 nm, which is impossible to manufacture using a conventionalmethod in which a contact is formed in a contact hole. Also, the contactformed according to an embodiment of the present disclosure has arelatively low resistance because a relatively wide contact can bemanufactured without forming a contact hole. Additionally, lithographyand dry etching processes required for forming a conventional contacthole are unnecessary and overall process control is relatively simple,while time and costs for manufacturing an MTJ cell are reduced.

As a result, according to an embodiment of the present disclosure, ahigh integrated memory cell can be obtained.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

1. A method of forming a magnetic tunnel junction (MTJ) cell,comprising: forming an MTJ layer on a substrate; forming an MTJ cellregion by patterning the MTJ layer; sequentially depositing aninsulating layer and a mask layer on the MTJ layer including the cellregion; exposing an upper surface of the MTJ cell region by etching themask layer and the insulating layer at the same etching rate; anddepositing a metal layer on the insulating layer and the MTJ layer. 2.The method of claim 1, wherein the MTJ layer includes a base layer thatis conductive, a lower material layer having magnetic properties, aninsulating internal MTJ layer, an upper material layer having magneticproperties, and a cap layer that is conductive stacked sequentially. 3.The method of claim 2, wherein the insulating internal MTJ film iscomposed of a material comprising aluminum oxide (Al₂O₃).
 4. The methodof claim 2, wherein the forming the MTJ cell region by patterning theMTJ layer comprises: depositing a hard mask on the MTJ layer; patterningthe hard mask by first dry etching; and forming the MTJ cell region bysecond dry etching the MTJ layer to a depth using the hard mask as anetch mask.
 5. The method of claim 4, wherein the patterning the hardmask comprises: coating a photo-resist on the hard mask with a sizecorresponding to the MTJ cell region; and etching the hard mask by thefirst dry etching using the photo-resist as an etch mask.
 6. The methodof claim 5, wherein the hard mask is composed of a material including atleast one material selected form the group consisting of SiO₂, Si₃N₄,fluorinated silicate glass (FSG), phosphorous silicate glass (PSG), andboron phosphors silicate glass (BPSG).
 7. The method of claim 5, whereinan etching gas used for the first dry etching includes a fluorine groupetching gas including at least one compound selected from the groupconsisting of C₂F₆, C₄F₈, and CHF₃.
 8. The method of claim 4, whereinthe MTJ layer is etched until the base layer is exposed.
 9. The methodof claim 4, wherein the etching gas used for the second dry etchingincludes BCl₃ as a main gas and Ar as an additive gas.
 10. The method ofclaim 4, wherein a width and length of the MTJ cell region are each lessthan 100 nm.
 11. The method of claim 4, wherein a thickness of the hardmask is in a range of 1000˜8000 Å.
 12. The method of claim 4, wherein athickness of the MTJ layer is in a range of 400˜1500 Å.
 13. The methodof claim 2, wherein a height of the insulating layer deposited on aregion outside the MTJ cell region is at least greater than a height ofthe cap layer of the MTJ layer.
 14. The method of claim 13, wherein theinsulating layer is composed of at least one compound selected from thegroup consisting of SiO₂ and Si₃N₄.
 15. The method of claim 13, whereinthe mask layer deposited on the insulating layer has a planarized uppersurface.
 16. The method of claim 1, wherein the etching the insulatinglayer and the mask layer comprises: third dry etching the insulatinglayer and the mask layer at the same etching rate; terminating the thirddry etching when the MTJ cell region is exposed; and removing aremaining portion of the mask layer.
 17. The method of claim 16, whereinthird dry of etching is terminated when a component of the cap layer isdetected.
 18. The method of claim 16, wherein the etching gas used forthe third dry etching includes at least one gas selected from the groupconsisting of C₂F₆ and C₄F₈ as a main gas and at least one gas selectedfrom the group consisting of Ar and O₂ as an additive gas such that theinsulating layer and the mask layer are etched at the same etching rate.19. The method of claim 16, wherein the removing the remaining portionof the mask layer uses an ashing method in which the mask layer isremoved by producing volatile reaction products-using oxygen.
 20. Themethod of claim 1, wherein the metal layer is composed of at least onemetal selected from the group consisting of Ti, TiN, Ta, and Al.
 21. Amagnetic tunnel junction (MTJ) cell formed in accordance with the methodof claim 1.